1. Field of the Invention
The present invention relates to a vacuum processing apparatus for performing a process such as film formation, etching, or the like with respect to a target object in a vacuum.
2. Description of the Related Art
In a step of manufacturing a semiconductor wafer, a one-by-one type CVD apparatus is used as a thin film formation apparatus for forming an insulating film or a thin silicon film on the surface of a semiconductor wafer. Such a one-by-one type processing CVD apparatus has an airtight processing chamber for performing film formation in a vacuum atmosphere, and a mounting table for holding the wafer is provided therein. An electrostatic chuck for chucking the semiconductor wafer is provided to the upper surface of this mounting table utilizing an electrostatic force.
Such an electrostatic chuck has a structure in which the upper and lower surfaces of a thin conductive member are in contact with insulating layers to sandwich the thin conductive member. The wafer is chucked and held by a Coulomb force or a Johnsen-Rahbeck force generated when a direct-current voltage is applied to said conductive member.
In a CVD apparatus, in order to assure uniformity in film formation, inplane uniformity in a target object, i.e., inplane uniformity of a temperature distribution is required. Conventionally, a heating unit for heating a target object to a proper temperature is provided in the processing chamber. As this heating unit, a heating unit is arranged on the lower surface side of the electrostatic chuck at a position away from the electrostatic chuck, and heat of a heating element of the heating apparatus is transferred to the above electrostatic chuck by radiation.
However, when the electrostatic chuck and the heating unit are provided away from each other, and a wafer on the electrostatic chuck is heated by heat radiated from the heating unit, the following problems are posed.
First, since heat from the heating unit is transferred by radiation, a high transfer efficiency cannot be obtained. In addition, this type of mounting table is normally provided in an airtight processing chamber set in a vacuum atmosphere of, e.g., 10.sup.-6 Torr. When the heating unit is set in the processing chamber, a heat transfer efficiency further decreases. For this reason, the heating unit must be set in an atmosphere out of the processing chamber.
As a heating unit having an improved heat efficiency, a heating unit in which e.g., a coiled heating resistor is provided on the object-mounting surface of the mounting table and heats a target object is known. In this case, however, since the heating element is close to a semiconductor wafer as a target object, the influence of the arrangement pattern of the heating element directly appears on the wafer. A uniform process cannot be performed due to nonuniformity of a temperature distribution on the basis of this. In the CVD apparatus, if such nonuniformity of a temperature distribution occurs, a uniform film cannot be formed.
Furthermore, since the mounting table on which the electrostatic chuck is placed and the heating unit are independently provided, the large number of members and a long time for assembly are required, resulting in an inevitable increase in cost accordingly.
In the one-by-one type CVD apparatus, a thin film must be uniformly grown on a semiconductor wafer as a target object. For this purpose, a reactive processing gas must be uniformly supplied onto the entire surface of the semiconductor wafer. Conventionally, in order to uniformly supply a reactive processing gas onto the entire surface of the semiconductor wafer, a shower head on which a plurality of holes are formed in a gas blow surface is provided to the top portion of the processing chamber.
When a processing gas is uniformly blown from the surface of the shower head opposing a target object by the conventional shower head, the flow rate of the processing gas tends to increase from the central portion of the target object to the end portion thereof. For this reason, a concentration boundary layer of the processing gas becomes thicker toward the central portion of the semiconductor wafer, and becomes thinner toward the end portion thereof. As a result, even if the processing gas is uniformly supplied from the gas blow surface of the shower head into the processing chamber, it is difficult to distribute the processing gas onto the reactive surface of the semiconductor wafer with a uniform concentration. Therefore, a film formation rate may be nonuniform.
The electrostatic chuck needs to be powered by a high voltage power supply, and the heating element for heating a target object needs to be powered by a power supply which can supply a high power, i.e., a so-called large current. As described above, however, since the CVD film formation apparatus performs a process in a vacuum atmosphere, discharge between conductive members tends to occur. In addition, heavy metal contamination to a target object may occur from an exposed wiring portion at a portion near a heater due to generation of a metal vapor. For this reason, wiring must be performed in the outer atmosphere. Therefore, since wiring requires a structure isolated from a vacuum atmosphere, the structure becomes complicated. Since this structure contacts a heating temperature atmosphere to a target object, good durability may not be kept. For this reason, not only the isolated structure becomes complicated, but also a cost increases due to need of such a structure.